The present invention is particularly suited for continuous form printers which handle continuous form media, such as paper, labels, or multi-part forms. The invention is also suited for many types of printers including impact printers such as dot matrix printers and band printers or non-impact printers such as laser printers and ink jet printers.
FIG. 1 shows a portion of a media feed system 10 used in conventional dot matrix printers. Media feed system 10 includes a pin drive mechanism 12, a platen 14, and media guide 16, and is used to advance media 18 (shown in phantom) through a printer and past a print element (not shown, but typically adjacent platen 14) which places characters or graphics onto media 18. For dot matrix printers, the print element consists of a dot matrix printhead. In other printers, the print element may be, for example, a rotating photosensitive drum used in laser printers, an ink jet assembly, a dot matrix shuttle configuration, a daisy wheel, or a band printing mechanism.
Media 18 is typically continuous, folded paper. Media 18 has a central or main body 20 with opposing side sections 22 and 24. Each side section 22, 24 is easily separable from body 20 along tear or separation lines 23 and 25, respectively. Separation, if necessary, usually occurs after the document has been printed.
Left edge section 22 has a linear array or row of circular drive perforations 26. Similarly, right edge section 24 has a linear array or row of circular perforations 28. Perforations 26 and 28 have substantially the same diameters and a center-to-center spacing "A" which is sufficient to mate with pins of the pin drive mechanism 12, as will be described below in more detail.
Pin drive mechanism 12, as shown, consists of a media feed tractor mechanism which includes left tractor drive 30 and right tractor drive 32 mounted parallel to each other along respective side portions 22 and 24 of media 18. Tractor drives 30, 32 are supported by a support bar or rod 34 which extends therebetween. A lateral adjustment feature 36 is provided to enable adjustment of the lateral distance between tractor drives 30 and 32 to accommodate different width paper and to provide alignment adjustment between the tractor drives. A common drive shaft 38 (illustrated as having a square cross-section) extends between tractor drives 30 and 32 and is operatively connected to a drive mechanism (not shown) for driving the tractor drives in synchronization with the printer system.
Tractor drive 30 includes a continuous drive belt 40 made of a semi-flexible strip material, such as rubber, plastic, or metal. Belt 40 includes pins 42 which have a circular cross-section and are typically conical or "egg-shaped". Pins 42 are spaced apart a distance which is preferably equal to the spaced distance "A" of perforations 26, 28 so that the pins can be inserted into perforations 26 of media 18. Likewise, tractor drive 32 includes a continuous drive belt 44 with pins (not shown) for insertion into perforations 28 along side 24. The pins of the tractor drives mate with perforations 26, 28 of media 18 and, as belts 40 and 44 are rotated, the pins advance media 18 through the printer preferably in a forward direction indicated by arrow 46.
Tractor drive 32 includes a hinged guide plate 48 mounted thereon which swings down over side portion 24 of media 18 for guiding the media through pin drive mechanism 12 and for maintaining the media in substantial engagement with belt 44. Guide plate 48 has a longitudinal slot 50 which permits passage of the pins on belt 44. Tractor drive 30 has a similar guide plate which has been omitted in this figure for purposes of illustration.
Pin drive mechanism 12 advances media 18 in a forward media feed direction as indicated by arrow 46 toward a printer throat, which is referenced generally by numeral 52. The printer throat is typically a narrow passage through which the media is guided prior to being exposed to the print element. In FIG. 1, the printer throat is defined by lower media guide 16, platen 14, and upper media guide 17 (not shown in FIG. 1 for purposes of clarity, but is shown in FIG. 3) disposed above lower media guide 16.
In normal operation, media 18 is advanced by pin drive mechanism 12 through printer throat 52 and around platen 14. Thereafter, the print element (such as a dot matrix printhead) places a desired image onto the media.
Unfortunately, the media sometimes does not pass cleanly through the printer throat, but instead "jams" or becomes caught in the printer throat as illustrated in FIG. 2. This jam causes a ripple or accordion effect to the paper as illustrated, and can cause tearing at this point. As paper continues to feed, more jamming and tearing occur.
Media jams are a problem that has plagued the printer industry since its inception. Media jams exist despite efforts to design sophisticated paper guide systems intended to prevent such jams. Additionally, the problem becomes more severe as printer speed and throughput increases.
Once a printer user experiences an inevitable media jam, the user first removes continuous form media 18 from the printer throat, and oftentimes, from the printer entirely. Unfortunately, when removing the media, a piece of the media may tear off and remain jammed in the printer throat as illustrated diagrammatically in FIG. 3 by crumpled piece 60 lodged within printer throat 56. In addition to pieces of media, foreign matter or debris may become lodged in the printer throat. The user then reloads the media and attempts to refeed it through the printer throat. Again, the media feeds improperly and becomes jammed in the printer throat as shown in FIG. 2 because piece 60, which is still lodged in printer throat 56, prevents the media from passing therethrough. The unload/refeed cycle is then repeated without success.
Once the user realizes that a piece of media is stuck in the printer throat, the user typically pursues one of two courses of action. One plan is to attempt to physically remove the piece of media stuck in the printer throat without disassembling the printer. As illustrated in FIG. 4, the user may attempt to dislodge the media piece using a thin instrument 62 such as a screwdriver, knife, file, or the like. However, the printer throat is usually located in a very difficult location to access, if not completely inaccessible, by the user. For the printer shown in FIG. 4, the printer throat may, for example, be positioned beneath platen 14 in a location inaccessible to instrument 62. More importantly, using a thin instrument 62 in an attempt to dislodge the media piece stuck in the printer throat can damage fragile components within the printer, including the media guides which define the printer throat. Such damage can result in significant repair cost and printer down time.
An alternative plan is to disassemble the printer by removing platen 14 to gain access to the printer throat. For unsophisticated users, this alternative involves a service call to the printer company's service representative. This can result in significant expense in terms of service costs and printer down time while waiting for a service representative to come and repair the printer. Even for the sophisticated user who is capable of disassembling the printer without the assistance of a service representative, printer down time still causes a tremendous inconvenience.
As may be appreciated from these examples, media jams present a significant problem in printers. Removal of such media jams may consume a significant amount of time while the user attempts to remove the jam using an instrument, or disassembles the printer. Moreover, present techniques for removing media jams may damage the printer.
The present invention provides a simple, inexpensive, and timesaving way to remove media jams from printers.